How about vitamin D in horses?
Not much is heard about vitamin D in horses. Usually it is assumed that horses can produce this vitamin themselves under the influence of sunlight. But what about horses that always wear a blanket? Or horses that spend a lot of time in the stable? What not everyone knows is that many horses have an extra need for vitamin D. For example, due to heavy training, old age, or summer eczema. We will give you an overview of everything about vitamin D in horses.
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6 August '21 • 4 min reading time
Vitamin D is important for:
- Bone formation and bone strength (a deficiency can lead to bone loss and rickets)
- Liver function and liver health
- Insulin sensitivity and preventing metabolic syndrome (EMS)
- A strong immune system
- Energy in muscles (a deficiency can lead to muscle weakness)
Problems in the body - of people and horses - often result in an increased use of vitamin D. In those cases, a horse also needs more vitamin D.
Your horse has a higher need for vitamin D when:
- Allergies and immune problems such as CPL, summer eczema
- Muscle fatigue
- Liver and kidney diseases
- Body acidification (metabolic acidosis)
- Growing (young horses and foals)
- Old age
- Heavy exertion
A vitamin D deficiency can occur when:
- A horse spends most of the day indoors
- A horse wears (UV-blocking) blankets during the day
- A horse has one of the above conditions
- In young or old horses
- In horses that have to work hard
- Excessive washing of the horse or use of sprays that dissolve skin oils
- A horse does not receive sun-dried forage
- A horse does not receive a balancer with vitamin D
- A combination of these factors
How does vitamin D work in the horse's body?
Vitamin D is actually not a vitamin, but a hormone. It is necessary for the absorption of calcium and phosphate and the formation of strong bones. There is also a link between a vitamin D deficiency and an increased risk of cancer. There are two types of vitamin D: vitamin D3 and vitamin D2. D3 is produced in the skin of animals, under the influence of sunlight. Vitamin D2 is created in plants that have been mowed and then exposed to sunlight: for example, in sun-dried hay. The main source of vitamin D for people, and for many horses, is the production in the skin under the influence of sunlight. D3. In horses, this production is slower than in people, especially in horses with darker colors. The main dietary source of vitamin D for horses is sun-dried grass. This contains vitamin D2. There is little or no D2 in fresh grass, as the vitamin is produced in the plant after cutting, when the grass is exposed to sunlight. It remains present in the sun-dried hay for a while, but the levels decrease in old hay that has been stored for example for a year. Also, if the hay dries less, as is the case with pre-cut silage, there will be less vitamin D2 in the hay. Older, longer, and mature grass contains more vitamin D2 than shorter, younger grass. Both vitamin D2 and D3 go through a number of 'activation steps' before they are actually used in the body. The liver processes the substances into so-called D metabolites, which are then distributed throughout the body in the blood plasma. The action of D2 and D3 is not exactly the same, it seems that D3 (from the sun or, for example, fish oil) works much more effectively than D2.
Vitamin D deficiency due to blankets?
Not much research has been done on the influence of blankets on the production of vitamin D. One small study in New Zealand with regular blankets showed a small difference between horses with and without blankets. In summer, there was clearly more vitamin D in the blood than in winter. The researchers therefore conclude that supplementing with vitamin D in winter may be a good idea. The difference between horses with and without blankets was not that big, but in New Zealand the UV intensity is much higher than in the Netherlands or Belgium - you also burn much faster as a human there. Moreover, it concerned regular blankets, which still let through radiation and not UV-blocking blankets that are often used nowadays. Finally, the horses in this study were healthy and were outdoors 24 hours a day. If your horse has a higher need for vitamin D, due to, for example, summer eczema, and always comes outside only with a UV-blocking eczema blanket, it may well be that he is also not getting enough vitamin D in the summer. It really differs per horse. Also, horses that spend a lot of time in the stable and do not receive sun-dried hay but packaged silage, can develop a vitamin D deficiency. Sprays against insects and frequent washing of a horse can also damage the oily natural protective layer of the horse's skin. This can lead to the horse producing less D3 on its own.
Summary: when should you supplement a horse with vitamin D?
Vitamin D is a very important vitamin for the bones, muscles, and immune system of horses. Healthy adult horses that spend the whole day outside and eat sun-dried hay will generally not have a vitamin D deficiency. Horses that are young, old, have immune problems, allergies, summer eczema, liver or kidney diseases, train hard, or spend the whole day in a stable or under a UV blanket can indeed develop a vitamin D deficiency. For these horses, a supplement may be a good idea. A balancer with highly concentrated minerals is always the basic supplement for horses.